(1) Field of the Invention
This invention relates to a delay line device for delaying signal transmission in a computer or a measuring apparatus and a method of producing the delay line device, especially to such a delay line device having an excellent frequency characteristic in a high frequency band of 100 MHz or above and a manufacturing method thereof.
(2) Description of the Prior Art
FIG. 1 shows a conventional delay line device having an excellent high frequency characteristic. The delay line device comprises an insulating plate 31, a strip-line conductor 32 formed on an upper surface of the plate 31, a grounding electrode layer (not shown) formed almost all over a bottom surface of the plate 31, a pair of grounding leads 34 connected to the grounding electrode layer, and input and output leads 35 and 36 respectively connected to ends of the strip-line conductor 32. The strip-line conductor 32 is used as a signal line.
In the above construction, extending a delay time requires extending the strip-line conductor. The extended strip-line conductor requires quite a large plate, which prevents the realization of a compact delay line device.
Japanese Patent Publication Kokai No. 1-143403 has disclosed a delay line device which can be compact. As shown in FIG. 2, a plurality of microwave IC boards and a plurality of insulating plates 41, 42 and 43 with no conductor are accumulated alternately. Each microwave IC board comprises an insulating plate 44, 45 or 46, a strip-line conductor 47, 48 or 49 formed on a main surface of the plate 44, 45 or 46 and a grounding electrode (not shown) formed all over the other main surface of the plate 44, 45 or 46. The strip-line conductors 47, 48 and 49 are connected in series via a through hole made of holes 51a, 51b and 51c and another via hole made of holes 51d, 51e and 51f. The total length of the connected strip-line conductors, which acts as a signal line, defines a delay time.
Such a delay line device can be compact due to the serial connection of the strip-line conductors. However, the grounding electrodes are connected by through-holes made of a plurality of holes 52 through 56 of each insulating plate. Since the holes should be made in such an area that have no influence on the electric characteristics of the strip-line conductor, each insulating plate should have an extra area for the holes. Accordingly, the compactness of such a delay line device is limited. Furthermore, strip-shaped leads used as input and output terminals have extra inductances, which deteriorate the high frequency characteristic of the delay line device.
The above delay line device are produced as follows. The baked microwave IC boards and unbaked insulating plates 41 through 43 with no conductor are accumulated alternately and bound with a binder. The binder possibly fluctuates the capacity between the strip-line conductors and the grounding electrodes, which also deteriorates the high frequency characteristic of the delay line device. Moreover, it is difficult to appropriately align the microwave IC boards and the insulating plates in the manner that the boards and the plates are connected easily. Producing the insulating plates and the microwave IC boards with many through-holes is also troublesome.